Introduction

SafeSol Ltd and Huwa-San

SafeSol Ltd introduced Huwa-San into the UK legionella control market in 2004 and have used it since that time. The chemical has found steady acceptance since that time as

  1. a competitor to chlorine for one-off water disinfections and
  2. a competitor to chlorine dioxide as a continuous dose chemical.

Like all innovative treatments Huwa-San has been opposed by traditionalists, by companies selling competitor disinfectants, and by companies using other me too silver stabilised hydrogen peroxides.

Huwa-San and Biofilms

This blog is written by our technical director Bob Wilson, who has been working with oxidising biocides since the 1970’s. This includes working with and studying Huwa-San[1], chlorine and chlorine dioxide. He has been involved in several expert witness cases including the Edinburgh Legionella Cooling Tower Outbreak.

It is the first blog in a series of 4 that will look at the efficacy of chlorine and chlorine dioxide compared to Huwa-San. This blog compares the efficacy of chlorine and how it reacts with biofilm compared with Huwa-San, a silver stabilised hydrogen peroxide.

[1] The stabilisation of Huwa-San allows it to delay the reaction between chloride in water and silver ion. This stabilisation is unique to the Roam Technology product, differentiating it from other SSHP formulations.

Chlorine and Biofilm: The Theory

Chlorine and Biofilm Penetration

Back in 1992 I got a phone call asking if my company could provide a chlorine dioxide dosing system for continuous dosing of the chemical into water. Up until that time I had spent 22 years using chlorine (gas and sodium hypochlorite solution) as the oxidising biocide of choice and had never heard of chlorine dioxide as a legionella control chemical. The hospital engineer making the request was adamant. He insisted on chlorine dioxide because he did not believe that chlorine was  effective against biofilm. He wanted to ensure his system was protected in the event that a legionella-based biofilm should develop in the pipework.[2]

This was pretty radical thinking in the early 1990’s. Biofilm research was scarcely in its infancy. Montana State Institute had just started their pioneering studies of Biofilm formation  Their early work however had shown that chlorine was not effective in dealing with established biofilm because of reactivity with the organics associated with biofilm and the slow diffusion of the chemical into the biofilm. [3] This work was carried out using a chlorine probe that detected chlorine concentrations within a biofilm and compared the chlorine concentration at various depths with in a biofilm compared with the chlorine concentration in the bulk liquid. I have referenced another paper[4] from the Montana State Institute below which confirms this. I could cite many more.

[2] The system was supplying water to a transplant unit. The main users of the water were patients with no immunity

[3] Direct Measurement of Chlorine Penetration into Biofilms during disinfection De Beer D. Srinivasan R and Stewart PS Montana State University. Applied and Environmental Microbiology Dec 1994 p 4339 -4344

[4] https://pubs.acs.org/doi/10.1021/es9509184-  Chlorine penetration into Artificial Biofilm Chen C and Stewart P

Chlorine and its reaction with Bacteria

Chlorine is an effective killer of free-swimming (planktonic) bacteria, so if applied continuously, at the correct concentration will prevent biofilms from forming. At the correct concentration chlorine may also remove a recently formed biofilm. However it will not penetrate, destroy, or remove an existing biofilm.

Behenke and Parker[5] showed that the efficacy of chlorine on clusters of biofilm detached from a surface biofilm was inversely proportional to the size of the cluster.

[5]https://aem.asm.org/content/77/20/7176

Why Does Chlorine remain the disinfectant of choice?

Despite this chlorine (generally based on sodium hypochlorite solution) is still the disinfectant of choice for domestic water systems, most cooling towers, swimming pools, spas, and hot tubs. These are all situations where biofilms form. Yet a Scottish NHS hospital engineer, almost 30 years ago, knew something then that many people today have still to learn

The Practice: Constant dosing of water systems

Nobody uses chlorine (Bleach) as a continuous dose chemical for domestic water systems. Chlorine dioxide, pioneered by NHS Lothian in 1992 is widely used throughout the NHS for disinfection of hot water systems as a disinfection where hot water temperature control cannot be achieved. Chlorine Dioxide is used because it will prevent biofilm formation but will also destroy existing biofilm.

The Practice: Shock disinfection of water systems

Huwa-San and other silver stabilised hydrogen peroxides would never have gained acceptance as a water system disinfection chemicals had chlorine been a consistently effective biofilm and legionella control chemical. The first use of Huwa-San was in a Liverpool night club, where despite, several chlorinations legionella returned to the water system. One Huwa-San disinfection removed the problem. This pattern has been  repeated on countless occasions and SafeSol have several case studies to demonstrate this.

Hospital

Conclusion

In systems with no or little biofilm, chlorination will probably be successful. The problem lies if there is a legionella based biofilm in a system. Chlorination will only attack the outer layers of the biofilm. It takes a number of days for the biofilm to recover. Therefore immediately following a chlorination, the sluggish biofilm, will not be sloughing or sending bacteria into the water. This results in low TVC levels (Total Viable Count- Levels of general bacteria) when samples are taken after chlorination. A few days later as the biofilm regenerates legionella bacteria will start to appear in the water again. Therefore the system can appear clean whereas in reality there is a legionella issue.

Bob Wilson’s next blog looks at chlorine dioxide as a biofilm remover.

SafeSol have worked with Huwa-San technology for over 20 years and have more than 75 years experience in water treatment. We are happy to help with any queries and provide technical support .

Call 0191 4478008 or info@safesol.co.uk